Two of the three towers are Orange County’s tallest, and now their owner can add another superlative: they’re among the nation’s greenest.

The Plaza Tower, O.C.'s tallest building

The three South Coast Plaza office towers gained a gold LEED certification for operations and maintenance from the U.S. Green Building Council earlier this year, an honor so far accorded only one other building in the nation. It took two years of tweaking and retrofitting to win the rating, which also earned a letter of recognition from the president’s office of environmental quality last week.

All three towers are owned by Henry Segerstrom, the Newport Beach millionaire and arts patron, and the Segerstrom family.

“We have just changed our whole outlook on how we approach the world,” said Stan Taeger, director of office property management at the towers for the past 35 years.

The changes made by Taeger and his staff mostly involved how the buildings are operated and maintained; no large-scale structural improvements were needed. While LEED certifications have been around for awhile, these are the among the first gold certifications for changing operation and maintenance practices in existing buildings.

“It’s all about whether or not that building is running efficiently,” said Betty Friedrichs, membership chairwoman of the U.S. Green Building Council chapter in Orange County. “How are they conserving water, what are they doing about reclamation of trash — and the way they are cleaned as well. We’re very proud of them, especially in conservative Orange County.”

The Center Tower, O.C.'s second tallest

The changes ranged from big to small. On the large end: changing when the water used for air-conditioning is chilled (at night) and how trash is recycled. At the smaller end: installing hands-free fixtures in the restrooms, or placing mats at the building entrances (less dirt tracked in means less vacuuming, hence less energy used to vacuum).

They started buying carpeting locally, instead of ordering it from Georgia, greatly reducing fuel costs and greenhouse gas emissions needed to transport them.

In the oldest building, the 17-story Park Tower that opened in 1979, they couldn’t use the water-chilling method because of its more conventional air-conditioning system. Instead, they started channeling outdoor air into the system on cool mornings, saving a bundle on energy costs.

The Plaza Tower, 21 stories high and Orange County’s tallest building, got an operational makeover, including an overhaul of its recycling program. Now, everything that is not wet waste is sent to a sorting facility for recycling, Taeger said.

The Center Tower, also 21 stories and the county’s second tallest building, switched to chilling water for the next day’s air conditioning at night, when power rates are lower. Aerators in faucets all three towers reduced water use, he said, and also prompted thanks from tenants because the faucets no longer splashed them when they washed their hands.

At the law firm located in the tower, Latham & Watkins LLC, managing partner Scott Shean said the changes were made so unobtrusively that no one in his office really noticed. The company had been conducting its own green programs, including reduction in use of paper.

Park Tower, the oldest of the three.

“We are proud, given the initiatives we were implementing in our firm, to be resident in a LEED-certified building,” he said.

Still, pursuing the certificate brought a new understanding for building managers.

“We’re running the buildings, not letting the buildings run us,” Taeger said.

And just how do these changes pencil out? Here are Taeger’s estimated yearly reductions and savings for all three buildings combined: